chemicals on clay liner

8/8/2019 Chemicals on Clay Liner

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Effects of Chemicals on CompactedClay Liner

Sanjeev SinghResearch Scholar, Department of Civil Engineering, IT, Banaras Hindu

University Varanasi-221005, IndiaEmail: [email protected]

Arun PrasadLecturer, Department of Civil Engineering, IT, Banaras Hindu University,

Varanasi-221005, IndiaEmail: [email protected]

ABSTRACTEngineering properties of bentonite soils get modified upon contamination with differentchemicals from industrial waste. Bentonite soil is often used as a material for clay liner. Butits engineering properties change when it is contaminated. To see the effect of inorganic &organic chemical on bentonite soil, two chemicals (Aluminium hydroxide and Acetic acid)that are generally found in municipal solid waste were selected. The effect of these chemicalson Bentonite soil has been studied in a controlled condition in the laboratory. . The optimumvalues of these chemicals are evaluated and added separately to Bentonite soil. The

engineering properties such as Differential Free Swell, Hydraulic Conductivity and SwellingPressure were found out. The result of differential free swell indicate that with Acetic acidand Aluminum hydroxide the free swell decreases by 47 % and 49 % respectively. Thehydraulic conductivity results show that it decreases by 12% with Aluminum hydroxide and17% by Acetic acid. Tests were also carried out to evaluate Shear strength parameters of Bentonite soil upon contamination with chemicals. The result of swelling pressure indicatedthat it decreased by 82% when Aluminum Hydroxide was added and increased by 20% whenAcetic Acid added was added, Maximum Dry Density decreased by 14.8 % when Aluminumhydroxide was added & 7% with Acetic acid, The strength parameters cohesion „c‟ and the

angle of internal friction (Ø) were also evaluated and was observed that cohesion decreases by50% with Aluminum Hydroxide and 43% with Acetic Acid, and angle of internal frictionalmost remain same. The selected soil is considered to be highly expansive in nature. Inaddition to these tests some test were also carried out to study the fabric of soil such asScanning Electron Microscope (SEM), Cation Exchange Capacity (CEC), Infra-RedSpectroscopy (IR), X



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INTRODUCTIONCompacted clay has gained wide acceptance as part of the barrier systems for municipal or industrialwaste disposal site (Rowe et al, 1995; Daniel & Koerner 1995; Rowe 2001). However, this acceptance

is largely based on experience in North America & Europe. There has been much less work conductedto examine the use of clay found in other part of world. Any such examination must involveconsideration of factors such as hydraulic conductivity, compaction, swelling pressure and shearstrength characteristics etc.The bentonite-based material being evaluated in several countries as potential barriers and seals for anuclear waste disposal system In order to investigate whether local Korean bentonite could be usefulas a buffer or sealing material in an high level waste repository system.( Jongwon Choi et al,2001).The interaction of minerals in bentonite soil with organic materials may result in changes of theirsurface properties and microstructures. Such changes are critical for the environment and should betaken into consideration during treatment of wastewater by clay materials. In the repositories of municipal waste, in addition to stable waste materials, some organic acids and bases are formed asproducts of chemical, photochemical and biological reactions (Acher and Saltzman, 1989; Lee Wolfe,

1989; Perry et al., 1989). Leakage waters trickling through municipal repositories contain organicbases and other polar water-soluble organic compounds, often accompanied by water insolublealiphatic or aromatic hydrocarbons (Yaron, 1989).A considerable amount of information related to contaminant has been published for constant chargedsoils formed in cold and temperate climates. However, there is only limited data on variable chargedsoils formed in tropical regions. In the present study an attempt has been made to have a betterunderstanding about the behavior of compacted clay upon contamination with different chemicals.Bentonite soil is used as the compacted clay liner and the chemicals used in the present study areAluminum hydroxide (inorganic chemical) and Acetic acid (organic chemical). Aluminum hydroxide[Al(OH)3] is widely used in the manufacture of fire retardants, fillers, pigments, adsorbents, catalystsetc. and also available in the waste generated during the manufacturing process. Similarly, Acetic acid[CH3COOH] is available in the waste product during the fermentation of organic substances. The

properties of Bentonite soil is presented in Table 1.

Table 1: Properties of Bentonite Soil

Silica 50.73 %

Alumina 20.40 %Ferric Oxide 5.78 %Titanium Dioxide 1.30 %Magnesium Oxide 1.74 %Calcium Oxide 1.07 %Magnous Oxide NilSodium Oxide 2.12 %Potassium Oxide 0.92 %

Loss on Ignition 15.90 %Gel Index 18%pH(2% suspension ) 7.2%



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EXPERIMENTAL PROGRAMCommercially available Bentonite soil is used for the entire tests. The samples for all the tests wereprepared by mixing optimum dose of the chemical and then compacting the mixture at optimum

moisture content (OMC). To simulate field condition, all the tests were carried out following theprocedure for the heavy compaction test. A comprehensive laboratory testing was then carried out onthe samples prepared in order to determine its mineralogical composition, geotechnical properties andphysico-chemical properties. Following laboratory tests were conducted on soil to determine its indexproperties and compaction, strength, and volume change characteristics:Determination of the fabric by the scanning electron microscopy (SEM) technique.X-ray (XRD) technique has been used for the determination of possible phases present in the soil.IR spectroscopy was carried out to get an information on fundamental vibrational modes of theconstituent units of the soil.Cation exchange capacity (CEC) and pH were carried out to study the physico-chemical nature of thesoil .CEC was done according to IS 2720 ( Part 24)-1987 and pH according to IS 2720 ( Part 26)-1987.

The consistency behavior was determined by the evaluation of Atterberg limits: as per IS-2720 (Part5)-1985.Heavy compaction test was carried out to investigate the compaction characteristics IS-2720 (Part 8) – 1983.Unconsolidated Undrained Triaxial compression tests on cylindrical specimens 3.81 cm in diameterand 7.62 cm long, for strength evaluation of soil IS-2720 (Part 11)-1971One dimensional consolidation test on samples 6.0 cm in diameter and 2.0 cm in thickness, forHydraulic conductivity analysisThe percentage of swell test was carried out in a consolidation ring of 6.0 cm diameter and 2.0 cmthick, to determine the volume change behavior of the soil. IS 2720(Part 40)-1977The swelling pressure test was performed using a constant volume condition using proving ringmethod. Test was carried out on samples of height 128 mm and 100 mm in diameter. The volume of

the sample was kept constant after flooding the soil with water as per IS (Part 41)-1977

RESULTS AND DISCUSSION

Mineralogical properties

Fabric

Geometric arrangement of particles in the soil is referred to as fabric of the soil. The fabric plays acrucial role in controlling the engineering parameters of soil. The scanning electron microscopytechnique was used to study the fabric of the soil at a magnification of 250X.



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(a) Bentonite (b) Bentonite + Aluminium Hydroxide

(c) Bentonite + Acetic Acid

Figure 1: SEM micrograph

Fig. 1(a) shows the micrograph of the Bentonite soil added with distilled water, Fig. 1 (b) shows themicrograph of soil added with Aluminum hydroxide, and Fig. 1(c) shows of soil added with Aceticacid. By studying the micrograph, it was observed that flocks are formed due to Acetic acid. In case of Aluminum hydroxide it forms crystalline silicates hydrates due to partial dissolution of Al(OH)3, which make the soil hydrophobic, which is significant in micrograph.

X-Ray Diffraction (XRD)The XRD test was done on SIEFERT MZ VI. The mineralogical identification was based on the XRDstudies carried out for identifying the reaction products formed.



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Figure 2: XRD of Bentonite with Chemicals

The XRD of bentonite soil alone is shown in 2(a). The XRD pattern of untreated bentonite indicate thepresence of montmorillonite, quartz etc.The XRD of bentonite soil mixed with Al(OH)3 is shown in Fig.2 (b) and with acetic acid is shown inFig.(2(c).

The XRD of bentonite soil mixed with Al(OH)3 and with CH3COOH does not show any markeddeparture in peaks when compared to XRD of bentonite soil alone. This shows that mineral phaseremains same upon treatment with both Al(OH)3 and CH3COOH.

Infrared Spectra (IR)The IR test was done on Varian 3100 FT-IR (Excalibur Series).Fig.3 shows the graphs of IR spectra inregion 4000-400 cm-1 that provides information on fundamental vibrational modes of the constituentunits of these materials. Graph-a shows IR obtained for bentonite only, graph-b is for bentonite +Aluminium hydroxide and graph-c is for bentonite + Acetic acid. OH stretching and bendingvibrations occurs in the spectral region of the 3750-3500 and 950-600 cm-1,respectively.Si-O and Al-Ostretching modes are found in the 1200-700 cm-1 range, while Si-O and Al-O bending modes dominatethe 600-400 cm-1 region.

a-Bentonite onlyb-Bentonite+AluminiumHydroxide

-



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Figure 3: IR-Spectra of Bentonite with Chemicals

The IR spectra indicate that montmorillonite is the dominant mineral phase in this clay. The absorptionband at 3624 cm−1 is due to stretching vibrations of structural OH groups of montmorillonite. Acomplex band at 1032 cm−1 is related to the stretching vibrations of Si – O groups, while the bands at529 cm-1 are due to Al – O – Si bending vibration. The band at 690 cm−1 was assigned to coupled Al – Oand Si – O out-of-plane vibrations. Water in montmorillonite gave a broad band at 3446 cm−1 corresponding to the H2O-stretching vibrations, due to an overtone of the bending vibration of water

observed at 1639 cm−1. The changes in the Si environment after acid activation process were reflectedin both the position and the shape of the Si – O stretching band near 1032 cm−1. A slight shift of thisband to higher frequencies indicates alteration of the structure. The IR spectrum of the Bentonite+Al(OH)3 shows, in addition to the tetrahedral Si – O band near 1033 cm−1, absorption band at1120 cm−1, assigned to Si – O vibrations of amorphous silica with a three-dimensional framework. Thespectrum of the Bentonite +Al(OH)3 sample, has all absorption bands characteristics of amorphoussilica (1120, 791 and 467 cm−1) confirms a high degree of structural decomposition. Almost same typeof spectra is seen in Bentonite + Acetic acid. The broad band near 1032 cm−1, assigned to complex Si –

O stretching vibrations in the tetrahedral sheet, upon saturation process moved to 1026 cm−1 in the Fig.3c, but some broadening and a decrease in intensity of the Si – O band was observed.

PHYSICO-CHEMICAL PROPERTIESThese properties are related to the physical and chemical interaction of the soil particles with eachother and with their environment such as the pore fluid and dissolved salts etc. For fine-grained soils,the physical interaction is of little importance. However, the behavior of fine-grained soils is entirelydependent on how the particles interact chemically with each other or with their environment. Variousphysico-chemical properties have been determined for uncontaminated and contaminated bentonitesoil and are presented in Table2.



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Cation Exchange Capacity (CEC)CEC of a clay can be defined as the amount of exchangeable ions, expressed in milliequivqlents, per100g of dry clay. The CEC of bentonite alone was determined by Ammonium acetate saturationmethod and is found to be 54.84 meq/100g where as CEC of Bentonite found by Yurdakoc, M. (2007)

is 92 meq/100g of clay. This difference in CEC may be due to variation in the mode of formation of bentonite. The CEC of bentonite alone and bentonite with chemicals is shown in Table 2. The CEC of bentonite + Aluminium hydroxide is 55.05 meq/100g and of bentonite + Acetic Acid is 43.05. There isa marked reduction in the CEC of the Bentonite when added with Acetic acid. However, withAluminum hydroxide it remains almost same.

Specific Surface Area

The surface of clay particles per unit mass is generally referred to as specific surface, usuallyexpressed in m2 /g. BET surface area was determined by nitrogen adsorption and desorption dataacquired on a Micromeritics ASAP 2020 apparatus. The sample was pretreated overnight undervacuum of 5X10-3 Torr @ 3500c for 15 hrs. Surface area measurement had an error of ±2 m 2 /g. Thespecific surface area of bentonite + Aluminium hydroxide is 136.33 m 2 /g and of bentonite + AceticAcid is 68.79 m2 /g. It was observed that there is an increase in surface area of bentonite + Aluminium

hydroxide and bentonite + Acetic acid over bentonite alone, which is also evident in micrograph of SEM. The results of specific surface are presented in Table 2.

pH

pH of the samples was measured by a pH meter. The results showed that there is a slight increase of pH, showing the basic nature of the chemical.

Table 2: Summary of Various Physico-chemical properties of bentonite soil andbentonite with chemicals.

Property Bentonite Bentonite+Al(OH)3

Percentageincrease(+)/ Decrease(-)

Bentonite+Acetic acid

Percentageincrease(+)/ decrease(-)

CEC (meq/100g) 54.84 55.05 (+)0.38 43.05 (-)21.5Specific Surface Area

(m2 /g)54.02 136.33 (+)152.37 68.79 (+)27

pH 6.56 7.66 (+)16.77 8.18 (+)24.70

GEOTECHNICAL PROPERTIESThe geotechnical properties were determined for bentonite, bentonite + Aluminium hydroxide andbentonite + Acetic acid. The geotechnical properties have been used to investigate the influence of microstructure and physico-chemical changes on the physical and mechanical behavior of thebentonite soil under investigation.

Atterberg LimitsThe optimal dose of the chemicals to be added is evaluated using Atterbergs Limits. When theplasticity index is decreasing the hydraulic conductivity increases and is maximum at minimum valueof plasticity index (Brandal H.,1992).The percentage of chemical corresponding to minimum plasticityindex is taken as optimum dose of chemical.

Compaction Test

Heavy Compaction test results indicate that addition of Acetic acid causes reduction in both OMC andMDD whereas addition of Aluminium hydroxide causes increase in OMC but reduction in MDD.



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Relative change in OMC and dry density will depend on the effect of resistance offered by soilparticles during compaction. This behavior can be explained in context of diffuse double layer. Withthe addition of Acetic acid, diffuse double layer tends to depress; this allows particles to come closerunder the same amount of compactive effort leading to increase in density. On the other hand, with the

addition of Aluminium hydroxide, maximum dry density decreases whereas OMC increases. Additionof Al (OH)3 forms crystalline silicate hydrates due to partial dissolution of Al (OH)3. This is due to thedissolution of Al (OH)3 that gives free ions which combine with alumina or silica to initiate complexAluminium silicate reaction that will make the soil hydrophobic and an increase in OMC (Gutschick,1978).

20 22 24 26 28 30 32 34 36 38 40 42 44

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D r y d e n s i t y ( g / c c )

Water content (%)

D r y d e n s i t y ( g / c c )

Water content (%)

Bentonite

Bentonite + Acetic acidBentonite + Aluminium Hydroxide

Figure 4: Influence of Chemicals on Compaction of Bentonite

Shear Strength Parameters

The results of undrained triaxial test performed on the samples prepared at OMC are presented inTable 3. Typical stress versus strain curves are presented in Figs. 5(a) to 5(c). Results indicate thatwith the addition of Aluminium hydroxide, the cohesion (Cu) decreased by about 50% whereas theangle of internal friction (Øu) remained unchanged. With the addition of Acetic acid, the behavior of bentonite was almost same as that with Aluminium hydroxide.



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Figure 5(a): Stress-Strain Curve of Bentonite alone

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2 )

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0 10 20 30 40 50 60 70 80

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Figure 5( b): Stress- Strain Curve of Bentonite + Aluminium Hydroxide

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Figure 5( c): Stress-Strain Curve of Bentonite + Acetic Acid



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Differential Free Swell (DFS

When compared with Bentonite DFS decreases by 49% with addition of Aluminium hydroxide and by47% with the addition of Acetic acid. . The results are presented in Table 3.

Swelling PressureSwelling pressure is the pressure applied by the swelling clays when their volume change is prevented.A load cell was used to record the increase in pressure after the addition of water. The sample wasthen inundated by water. Since the sample was being prevented from undergoing any change in itsvolume, in reaction, it applies pressure to the load cell, which was recorded and is presented in Table3. It is observed that swelling pressure tends to decrease when Aluminium Hydroxide is added tobentonite soil and the behavior is same with Acetic acid also. Relationship between swelling &swelling pressure versus square root of time has been plotted and shown in Figs.5 (a) to 5(c).



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Figure 6: Influence of Chemicals on Swelling Pressureand Swelling of Bentonite soil



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The swelling pressure of bentonite only was 1.46 kg/cm2, whereas swelling pressure of bentonite +Aluminum hydroxide was 0.22 kg/cm2 and for bentonite + Acetic acid was 1.55 kg/cm2. There is adecrease of 85% when Aluminum hydroxide was added and when Acetic acid was added there is anincrease of 6%. It is observed that the above relationships are more or less mirror image of each other.

This suggests that during the ingress of moisture, development of swelling pressure corresponds tothat of swelling tend to stabilize with time. Swelling pressure is related to development of diffusedouble layer. Less value of swelling pressure is in case of Aluminum Hydroxide and can beconsidered as an indication of well-developed diffuse double layer.The rate of swelling in the initial stages was very high. This behavior is probably due to the dispersedsoil fabric. Individual particle surfaces were open to adsorb water. The water around the sample comein contact with the top and bottom surfaces of the sample. This interaction caused the fabric to changeslowly.

HYDRAULIC CONDUCTIVITY

The hydraulic conductivity of bentonite soil is normally in the range of 10-4

to 10-6

cm/sec and is saidto be impervious/slightly pervious soil. As such, the hydraulic conductivity is obtained by indirectmethod from the results of oedometer test.The test results indicate that, the hydraulic conductivity of bentonite is 1.06x10 -5 cm/sec. With theaddition of the chemicals, the hydraulic conductivity decreased slightly in both the case.

Table 3: Summary of Various Geotechnical properties of contaminated anduncontaminated bentonite soil

Property Bentonite Bentonite+Al(OH)3


Bentonite+Acetic acid


Liquid Limit (%) 220 345 (+)57 115 (-)48Plastic Limit (%) 53 50 (-)6 35 (-)34

Plasticity Index (%) 167 295 (+)77 80 (-)52Heavy

CompactionTest

MDD (g/cc) 1.44 1.29 (-)10 1.34 (-)7OMC (%) 29.0 30.5 (+)5 25.5 (-)12

ShearStrength

parameters

Cu (kg/cm2) 1.5 0.75 (-)50 0.85 (-)43Φu (Deg.) 16 16 -- 17 (+)6

DFS (%) 976 500 (-)49 516 (-)47Swelling pressure

(kg/cm2)1.46 0.22 (-)85 1.55 (+)6

Hydraulic Conductivity(cm/sec)

1.06x10-5 0.932x10-5 (-)12 0.88x10-5 (-)17

COMMENTSThe results of the above tests show that Aluminum Hydroxide is probably creating much moreseparation between diffuse double-layer of clay particles, which is causing breaking of the particlesinto smaller pieces and hence particle size is decreasing. This may be incursion of cations in double



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layer causing repulsion due to positive charge of double layer. However Acetic acid is not showingthis type of effect, and just causing increase of the particle size and appears that probably hydration istaking place in soil. This is also supported by XRD graph, which shows that some type of hydration istaking place, which is causing more ordered geometry in comparison to bentonite

CONCLUSIONSThe following conclusions can be drawn from the above discussion:

Acetic acid upon contact with bentonite soil leads to the formation of flocs. This is alsoevident from the reduction in hydraulic conductivity by about 17%. But when Aluminumhydroxide is in contact with bentonite soil, flocs reduced in size. As such the specific surfacearea increased.

XRD diffractogram of bentonite with Aluminum hydroxide and Acetic acid does not show any

marked departure in peaks when compared with XRD diffractogram of bentonite soil alone.Hence, it can be concluded that the mineral phases remain same, i.e. mainly montmorilloniteand quartz.

IR spectra of bentonite with Aluminium hydroxide and Acetic acid does not show any markedchange in fundamental vibrational modes of the constituents units. However in case of bentonite + acetic acid the peak at 1026 cm-1 is missing. This is probably due to some newbonding.

CEC decreases in case of bentonite + Acetic acid by 21.5% over bentonite alone. However incase of bentonite + Aluminium hydroxide there is negligible increase of 0.38%.

OMC and MDD, both show a reduction when bentonite is added with Acetic acid. But uponaddition with Aluminium hydroxide, MDD reduces but OMC shows an increase by 5%.

Strength parameter „c‟ decreased by 50% upon addition of Aluminum hydroxide to bentonite

and by 43% with Acetic acid. There is practical no change in the strength parameter „ Φu’ inboth the case, i.e. bentonite + Aluminum hydroxide and bentonite + Acetic acid.

When compared with bentonite, DFS decreases by 49% with addition of Aluminiumhydroxide and by 47% with addition of Acetic acid. It is observed that swelling pressure tendsto decrease when Aluminium Hydroxide is added to bentonite soil and the behavior is samewith Acetic acid also. This is also evident from Specific surface data.

Hydraulic conductivity decreases by 12% with Aluminum hydroxide and 17% with Aceticacid. This is also evident as the specific surface is increasing in both the case.

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In: Gerstel, Z., Chen, Y., Mingelgrin, U.,Yaron, B. (Eds.), Toxic Organic Chemicals in PorousMedia.Springer Verlag, Berlin, 1989, pp. 302 – 319.

2. Brandl,H. (1992),Mineral Liners for Hazardous Waste Containment, Geotechnique, Vol.42,No. 1.pp 57-65.



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3. Carson, D.A. (1995) “US EPA Experiences with Geosynthetic Clay Liner,” Geosynthetic ClayLiners, Koerner, R.M., Gartung, E. and Zanzinger (eds.),A.A. Balkema, Rotterdam,Netherlands,pp.17-30.

4. Dollhopf,D.J., S.C. Smith (1989) “Effects of Phosphogypsum and Magnesium Chloride,

Amendment on Abandoned Bentonite Soil, Proc. Of Reclamation, A Global Perspective,American Soc. Surface Mining and Reclamation and Canadian Land Reclam.Association, pp555-562.Calgary, Alberto,Canol.

5. E. Eren and B. Afsin (2007) “An investigation of Cu(II) adsorption by raw and acid- activatedbentonite: A combined potentiometric, thermodynamic, XRD, IR, DTA study”,Journal of Hazardous material,Direct science, June.

H. U. Rehman, S.N. Abduljauwad, T. Akram (2007) “Geotechnical Behavior of Oil-ContaminatedFine Grained Soils”Electronic Journal of Geotechnical Engineering,.

6. Jongwon Choi , Chul-Hyung Kang , Jooho Whang (2001) “Experimental Assessment of Non-

Treated Bentonite as The Buffer Material of a Radioactive Waste Repository” Journal of Environmental Science and Health, Part A, Taylor & Francis publication, May.

7. LeeWolfe, N.(1989) “Abiotic transformations of toxic organic chemicals in the liquid phaseand sediments”. In: Gerstel, Z., Chen, Y.,Mingelgrin, U., Yaron, B. (Eds.), Toxic OrganicChemicals in Porous Media. Springer Verlag, Berlin, pp. 136 – 150.

8. Perry, A.S., L. Muszkat, R.Y. Perry (1989) “Pollution hazards from toxic organic chemicals.”In: Gerstel, Z., Chen, Y., Mingelgrin, B., Yaron, B. (Eds.), Toxic Organic Chemicals inPorous Media Springer Verlag, Berlin, 1989, pp. 16 – 33.

9. Sadana, M.L. (1998) “Influence of Soil Type & Pore Fluid on Swelling & Swelling Pressure”,IGC-98,Vol.1,pp 37-41.

10. Sridharan A., M.R. Sudhakar & V.S. Gajarajan, (1987), “Effect of Caustic SodaContamination on Volume Change Characterstics of Bentonite”, Proceedings Cong. Onprediction & performance in Geotechnical Engg., Calgary, pp 347-35.

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Charactrization of Cr- and Fe- Pillared Bentonite by Using Crcl3, Fecl3, Cr(acac)3 andFe(acac)3 as Precursors”, Microporous and Mesoporous Material, Elsevier publication, July

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